You can use a keg as a secondary fermenter. Since the secondary fermentation is only for clearing purposes, it will not generate enough pressure to require an airlock.
To do this:
- First, clean and sanitize the receiving keg and fill it with water. Connect your CO2 tank to the receiving keg and push all the water out through the tap. Now you have an empty keg filled with CO2. It’s best to keep the keg under low pressure, around 3–5 psi.
- Connect your CO2 tank to the Corny keg with homebrew in it, keeping the pressure the same as in the receiving corny keg. Make a jumper line by attaching two “beer out” fittings (These are the black connects on ball lock Cornelius kegs) to both ends of a length of beer line tubing.
- Attach the jumper line to the “beer out” posts on both homebrew kegs (the post that connects to the dip tube). To transfer the beer, release the pressure from the receiving keg. The simplest way to do this is to attach a “gas in” fitting (the grey connect) to the “gas in” post and let the keg vent. This is why you want only a small amount of pressure on the keg. Beer will move up the dip tube and out of the first keg and down the dip tube and into the second keg.
- Remove the connectors once the keg is full and there you have it— a transfer in which the beer is not exposed to oxygen. Actually, a tiny amount will diffuse into the receiving keg against the flow of CO2 out the keg, but not much.
- If you are using the same process to transfer beer from a secondary fermenter to your serving keg, the first little bit of beer transferred will be very yeasty. The pickup tube will suck in yeast sediment at the bottom of the secondary fermenter and transfer it to your serving keg.
- To eliminate this, just watch the tubing and disconnect the jumper line once the beer changes from cloudy to clear. Connect your CO2 tank and a cobra tap to the receiving tank and blow out the yeasty beer.
- Then reconnect your setup and transfer the clear beer.